Articulated Valve Gear Question

[Sean R Das]

Hi. I am a steam buff who is thoroughly familiar with the anatomy of a locomotive, but while looking through Model Railroader's Cyclopedia Volume 1: Steam Locomotives, I was baffled by something:

In looking at pictures of some articulated locomotives, I often see the reachrod/power reverse gear connected to the rear valve gear only. Only few locomotives, like the GN 2-6-6-2 of 1906 and the N&W artics, have visible linkages linking the reverse shafts on both engines (usually underneath the locomotive), while others, like the UP Challengers (both early and late) have no such visually-evident connections.

My assumption is that linkages between the valve gears on the front and rear engines are hidden in places not visible even in the drawings. Am I right?

 

[Bob]

I've never actually worked on the valve gear on an articulated, so I can't say this with 100% certainty.

That said, there must be some connection. Articulated locomotives are essentially two engines under one boiler. They act independently, and one can slip by itself. So there has to be some kind of mechanical connection between the valve gears.

My GUESS (and it is a guess) is that the connection is insider the drivers, centered in a manner that accomodates the motion of the movable engine without having it affect the setting of the reverse gear. Probably something like how the brake rigging is attached to a truck to allow it to pivot.

 

[Eastsider]

Being a novice, I am trying to understand this question a little better for my own edification.

On an articulated locomotive, each "engine" is independent, and they are not synchronized (as Bob said). And each cylinder had its own valve gear. That much I understand.

So do I understand that the question is, how are the two valve gears for each "engine" linked?

 

[Bob]

So do I understand that the question is, how are the two valve gears for each "engine" linked?

That is correct. While there are two engines (the proper term for the pistions, wheels and valve gear etc) there is only one reverse lever in the cab. You'd always want both valve gear assemblies set to the same setting, i.e. forward or reverse, and how far they're hooked up.

The back engine is simple, since it's stationary. The rigging runs just like it does on any other steam loco (or so I presume). It's how the reverse rod gets to the front valve gear that's the question. If you did it conventionally, the first time you hit a curve things would turn into spaghetti.

 

[CGW101c]

Give me a couple of days. I'll try to get over to Kenefick Park here im Omaha to photo the Big Boy's Valve gear for you.

 

[CGW101c]

IT looks like there is a rod or link that runs from the center of a rod that connects the left and right side of the rear gear to the center of the rod that connects the right and left of the front gear. seems to run down the centerline of the boiler just above the frame. Still haven't got to the park yet. tom

 

[Zoohogger]

My 2 Cents and Photos

Here is the front and rear engine of Deep River Logging #7.

On the front engine photo,(inside the building) you see the reverse lever linkage and the shaft that runs across the engine is curved down in a crank shape. At the bottom of the crank is linkage that runs back to connect with the rear. On the rear engine photo I am pretty sure the lever that is almost straight up is connected to Johnson bar or power reverse. I believe that the connecting lever runs through the hole centered between the cylinders with a crosshead type setup.

Great set of Photos there, Ragnar. You were putting yours up the same time I was posting mine. You can see it much better on the 11.

 

[Ragnar]

Great set of Photos there, Ragnar. You were putting yours up the same time I was posting mine. You can see it much better on the 11.

Thanks!

I don't know anything about steam locomotives, so I hope these photos show the right equipment.

I am still trying to figure out how that linkage pivots when the front engine swings to the side on a curve. Can someone explain?

 

[shay2305]

I am still trying to figure out how that linkage pivots when the front engine swings to the side on a curve. Can someone explain?

If you look at the photo posted by Zoohogger of the rear engine from #7 you will see a square hole on the centerline of the engine just above the level of the cylinders. This hole houses a crosshead that connects the front and rear valve gear. The rod that heads forward is attached to the crosshead with a vertical pin which allows the rod to pivot with the front engine when is goes around a curve.

Hope this helps

 

[Ragnar]

Good explanation, Aaron. I understand how it works now.

 

[Ragnar]

Question:
What is the large pipe directly below that linkage? Looks to be about 5" diameter or so. Is that the air pipe?

 

[Dale001]

If i understand the pipe you are asking about it is the steam delivery pipe connecting the high presure cylinders to low presure cylinders.

 

[Ragnar]

Ok, thanks Dale, now I get it. The pipe carries exhaust steam from the HP cylinders of the rear engine, to the LP cylinders of the front engine.

Like the valve gear, it has a swivel design. Wikipedia says this:

"Steam was fed from the steam dome down to the aft, high-pressure cylinders - the exhaust steam from those being fed forwards in a pipe with a swiveling joint - to the forward, low-pressure cylinders."​